Not a problem, yes, the back comes this winter- it too will be reduced and cleaned out.
Minogame, well not exactly. The soil breaks down in all trees and over time the tree will need to have all of the old soil removed again, and again, and again. Just not on as aggressive a repotting cycle.
Crust. Understand, biut the large particles remaining, the hyuga and volcanic fall away as the roots are manipulated. The tree in the picture never freezes solid, the soil doesn't freeze, so the breakdown is due to the roots growing into the akadama particles and fracturing them and breaking them down. the picture shows it about as clean as we go on a pine, maybe a light rinse afterwards. Don't think the roots penetrate the particles? I received a Rocky Mountain Juniper from a friend in Southern texas to rescue. When I got the tree loaded into the back of my truck, the first thing I noticed was that it wan't secured in the pots I wrapped some 4 mm Aluminum wire around the pot and tied to the tree and stabilized it. The following spring I cut the stabilizer wires, cut the tie down wires and lifted the tree out of the massive pot it was in. I had noticed that the tree wasn't as heavy as I thought it might be, when I lifted the tree up, I noticed it had about 4" of a conventional haydite based potting mix, and below the potting mix was a 6" deep layer of styrofoam packing peanuts. Because of the wobble, the roots had not filled the pot, but the roots had aggressively grown down through the bonsai mix and into the peanuts. Interestingly, the roots had grown through the peanuts, not around them, so when you held the tree up, the roots hanging down were all supporting packing peanuts like beads on a string. I imagine the packing peanuts would work just fine, if you had the tree anchored in to the pot so that it would not wobble and break off the new roots.